Aristoteles was as great a hero in zoology as he was in botany, and he may be said to have founded the science. Certainly, some of the principal divisions of the animal kingdom were taught by him. He was the first to make an attempt to explain the anatomy of animals, the functions or duties of different parts of their bodies, and to compare them with those of man. He discussed their resemblances and differences with great acuteness. He was especially distinguished as a student of fishes, making a vast number of observations of his own, and collecting those of other writers. After much consideration, Aristoteles wrote upon the distinction between living things and inanimate nature, and we owe him the notion of the distinctions between the genus and the species. He wrote with regard to the species: “An animal species is an assemblage of individual animals, in which not only the whole form of any one resembles the whole form of any other, but each part in any one resembles the corresponding part in any other. Thus, every horse not only resembles every ether horse generally, but the eye or the hoof of every horse resembles the eye or hoof of every other horse. They are, therefore, the same in the character of the individual parts.” “A genus is an assemblage of individuals in which any one bears, upon the whole, an obviously perceptible resemblance to any other. But the corresponding portion in the different species of the same genus, usually differ in colour, form, numbers, size, and proportion.” This is not so clear as the notion of the species, and he extended the term genus to what is now called an assemblage of genera, that is to say, a family, order, or class. He clearly distinguished between white-blooded and red-blooded animals, and was aware of the mysterious connection between the existence of a spinal column, made up of bones, or vertebræ, and red blood. He makes vertebrated, or backboned, animals to take the first place in his scale of classification. Classifying man, viviparous and oviparous quadrupeds, birds, fishes, cetaceous animals (whales), and serpents amongst the red-blooded, Aristoteles put down as white, or no blooded animals, insects, or creatures divided into segments, cuttlefish, with soft substance, rather soft-shelled animals, like lobsters, and hard-shelled creatures such as oysters. He examined, one by one, all the species he could procure, and then classed together as a subordinate generic group all those, which resembling each other in the more important parts of their structure, differed only in size or colour, or in other points of little importance. Aristoteles founded the natural history of his age, and no one came near to him. He left nobody behind to follow his work.